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Post subject: Bullet Reverb ressurection
Posted: Tue Apr 11, 2017 6:52 pm
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So I got in too deep on this one, but it had a happy ending.
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This amp came in blown. I couldnt find the TDA2050 output chip locally, so I ordered a couple from China.
3 weeks later I get two chips in, put it together, sent it out.
Came back a week later blown again.
Put in the second chip and sent it out
Came back a week later blown again.
OK, they must all be fakes. Thats why no one reputable sells them. Now what? Im in a warranty situation and need to figure this out.

So I installed a TDA2030v. This is a lower power version of the same TO-220package. It is limited to +-18 volts at 15 watts.
To power it, I thought about Stratle52's trick with zeners to lower the B+. Then I though about getting a couple voltage regulators. Both mods produce a lot of heat and cut up the board.
Then I found a project transformer hanging around that looked good. It has a 24vac ct with 2 amp rating. It gives a stable +-18 volts to the new amp chip. I siliconed over the 120VAC solder terminals after hookup for safety.
Then I had to rebuild the traces around the reverb connectors on the main board. I battened them down with hot melt glue
Everything seems to run well. Nice sound for a small amp. Im crossing my fingers and sending it back.


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Post subject: Re: Bullet Reverb ressurection
Posted: Tue Apr 11, 2017 8:03 pm
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Tim, a lot of work. I've kinda given up on solid-state amps. After my 6 month run-in with a Conrad-Johnson monster. Those things have regulator circuits up-the-butt. I really need to get a good scope...

Do you have one of those new small footprint O-scope? Like a Tektronix 1052?

Thanks!


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Post subject: Re: Bullet Reverb ressurection
Posted: Tue Apr 11, 2017 9:14 pm
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I'm not in it for myself. At this point its just pride to make me deliver a working unit to a customer. They trusted me to fix it. I charged them. It didn't hold together twice.

I have an old Tek 465 CRT scope. I can put it on a 500 volt plate supply and not worry it'll go up in smoke. I inheireted it from an old British tech. RIP Norm Hogarth. Thank you. Its a little tired but I think we'll both make it to retirement this summer.


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Post subject: Re: Bullet Reverb ressurection
Posted: Tue Apr 11, 2017 10:20 pm
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This is a great allegory that illustrates precisely my point about anyone thinking about buying one of Fender's older-generation solid-state amp models. While generally great designs, the parts chain has dried up and it's hit-or-miss finding suitable repair components when they eventually crap out. Tim, I commend you for your efforts -- really herculean when all things are considered. But you and your diligent talents are the exception rather than the rule and while this episode had a happy ending, there are a myriad of others that do not. Take heed folks. For your *primary* amp, find one that's both reliable AND logistically-supportable.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Bullet Reverb ressurection
Posted: Wed Apr 12, 2017 2:03 am
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Great job TimsAudio, you are the best .


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Post subject: Re: Bullet Reverb ressurection
Posted: Wed Apr 12, 2017 8:59 am
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The amp repair biz is full of unobtanium. There's always another pile to step in as the amps come and go. Ya learn as ya go and don't step in that pile again. You can be sure that when I see another tda2050, I'll be running in the other direction.
The 2030 is a common 15 watt to220 package. They are in a lot of practice amps and are reliable.
The 2050 is a 30 watt version. I haven't run across before.
Its a small package to be dissapating that much heat. I can see why it was discontinued. The fakes were probably retagged 2030s.

Other bits of unobtanium are NE570 compressor chips found in many early pedals, all the tubes in early Ampegs, A/D converters in early synths. BBD chips in old delay pedals. Transistors in old amps. Its like a minefield in the repair landscape. You don't know you triggered something until yer a step and a half into it..


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Post subject: Re: Bullet Reverb ressurection
Posted: Wed Apr 12, 2017 9:37 am
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TimsAudio wrote:
...all the tubes in early Ampegs...


Amen to that!

I've never even heard of a 6146B (as originally specified for the SVT) let alone seen one. And the supply of quality 7027A's is all but exhausted now.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Bullet Reverb ressurection
Posted: Wed Apr 12, 2017 5:46 pm
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Retroverbial wrote:
TimsAudio wrote:
...all the tubes in early Ampegs...


Amen to that!

I've never even heard of a 6146B (as originally specified for the SVT) let alone seen one. And the supply of quality 7027A's is all but exhausted now.

Arjay


The 7027A is a great tube. Makes a big, big sound. Last 7027A I worked on, was an Ampeg V22. Boy, that was a loud, very good sounding combo.

The 6550 is harder to find, too. I haven't tried any of the newer Russian made ones. Last 6550 amp I worked on was a mono hi-fi amp that took eight (!) 6550 per channel. Two matched octet sets of Svetlana 6550s!


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Post subject: Re: Bullet Reverb ressurection
Posted: Wed Apr 12, 2017 6:29 pm
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The 7027a was recently added to the roster of JJ power tubes.
I just installed a pair in a B18N.


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Post subject: Re: Bullet Reverb ressurection
Posted: Wed Apr 12, 2017 7:05 pm
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How do they compare to vintage bottles from RCA, Raytheon, GE, Tung-Sol, etc?

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Bullet Reverb ressurection
Posted: Thu Apr 13, 2017 8:20 am
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My ears don't know how they compare. My musician customers who do, tell me JJs are more musical than other power tubes. So I expect the 7027s to be good sounding.
Better than NOS? I doubt it. But whats out there is mostly old old stock. used tubes that are already worn and possibly microphonic, certainly not replaceable from that supplier.
The best thing about the new tubes is availability and warranty replacements. If you want an old Ampeg, you can't be choosy about tubes. The JJs fill a hole.
Now if they would just build a 7199 tube. Ampeg, Gibson and Dynaco owners would cheer.


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Post subject: Re: Bullet Reverb ressurection
Posted: Thu Apr 13, 2017 1:57 pm
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TimsAudio wrote:
Now if they would just build a 7199 tube.


+1

Years ago I bought a really pristine Ampeg Gemini G15 with the intent to flip it for a profit. When I realized that the phase inverter was a 7199 and that they were OOP I prayed that it would hold together long enough for me to resell it. Eventually I did, quadrupling my investment. But it was still nip-and-tuck until I successfully unloaded it. I've since learned that a 6GH8A can be subbed for a 7199 by altering the socket pin-out or using a special adapter.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Bullet Reverb ressurection
Posted: Thu Apr 13, 2017 6:03 pm
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TimsAudio wrote:
Now if they would just build a 7199 tube.


Sovtek distributed a version of the 7199, a few years ago. It was terrible. No longer being made.

:(


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